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Time has been studied by philosophers and scientists for 2,500 years, and thanks to this attention it is much better understood today. Nevertheless, many issues remain to be resolved. Here is a short list of the most important ones: What time actually is; whether time exists when nothing is changing; what kinds of time travel are possible; why time has an arrow; whether the future and past are real; how to analyze the metaphor of time’s flow; whether future time will be infinite; whether there was time before the Big Bang; whether tensed or tenseless concepts are semantically basic; what is the proper formalism or logic for capturing the special role that time plays in reasoning; what are the neural mechanisms that account for our experience of time; whether there is a timeless nature “beyond” spacetime; and whether time should be understood only in terms of its role in the laws governing matter and force. Some of these issues will be resolved by scientific advances alone, but others require philosophical analysis.
Consider this one issue upon which philosophers of time are deeply divided: What sort of ontological differences are there among the present, past and future? There are three competing theories. Presentists argue that necessarily only present objects and present experiences are real, and we conscious beings recognize this in the special “vividness” of our present experience. The dinosaurs have slipped out of reality. However, according to the growing-universe or growing-block theory, the past and present are both real, but the future is not real because the future is indeterminate or merely potential. Dinosaurs are real, but our death is not. The third and more popular theory is that there are no significant ontological differences among present, past, and future because the differences are merely subjective. This view is called “the block universe theory” or “eternalism.” (Continue article)